Blood coagulation is a process consisting of a complex interaction of various blood components (or factors) that eventually results in a fibrin clot. Generally, the blood components participating in what has been referred to as the “coagulation cascade” are proenzymes or zymogens, i.e. enzymatically inactive proteins that are converted into an active form by the action of an activator. One of these coagulation factors is FVII.
FVII is a vitamin K-dependent plasma protein synthesized in the liver and secreted into the blood as a single-chain glycoprotein with a molecular weight of 53 kDa (Broze & Majerus, J. Biol. Chem. 1980; 255:1242-1247). The FVII zymogen is converted into an activated form (FVIIa) by proteolytic cleavage at a single site, R152-I153, resulting in two chains linked by a single disulfide bridge. FVIIa in complex with tissue factor (FVIIa complex) is able to convert both factor IX and factor X into their activated forms, followed by reactions leading to rapid thrombin production and fibrin formation (Østerud & Rapaport, Proc Natl. Acad Sci USA 1977; 74:5260-5264).
FVII undergoes post-translational modifications, including vitamin K-dependent carboxylation resulting in ten γ-carboxyglutamic acid residues in the N-terminal region of the molecule. Thus, residue number 6, 7, 14, 16, 19, 20, 25, 26, 29 and 35 shown in SEQ ID NO:2 are γ-carboxyglutamic acids residues in the Gla domain important for FVII activity. Other post-translational modifications include sugar moiety attachment at two naturally occurring N-glycosylation sites at position 145 and 322, respectively, and at two naturally occurring O-glycosylation sites at position 52 and 60, respectively.
The gene coding for human FVII (hFVII) has been mapped to chromosome 13 at q34-qtr 9 (de Grouchy et al., Hum Genet. 1984; 66:230-233). It contains nine exons and spans 12.8 Kb (O'Hara et al., Proc Natl Acad Sci USA 1987; 84:5158-5162). The gene organisation and protein structure of FVII are similar to those of other vitamin K-dependent procoagulant proteins, with exons 1a and 1b encoding for signal sequence; exon 2 the propeptide and Gla domain; exon 3 a short hydrophobic region; exons 4 and 5 the epidermal growth factor-like domains; and exon 6 through 8 the serine protease catalytic domain (Yoshitake et al., Biochemistry 1985; 24: 3736-3750).
Reports exist on experimental three-dimensional structures of hFVIIa (Pike et al., PNAS. U.S.A., 1999; 96:8925-30 and Kemball-Cook et al., J. Struct. Biol, 1999; 127:213-223); of hFVIIa in complex with soluble tissue factor using X-ray crystallographic methods (Banner to et al., Nature, 1996; 380:41 and Zhang et al., J. Mol. Biol, 1999; 285: 2089); and of smaller fragments of hFVII (Muranyi et al., Biochemistry, 1998; 37:10605 and Kao et al., Bio-chemistry, 1999; 38:7097).
Some protein-engineered variants of FVII have been reported. See, e.g., Dickinson & Rut; J Bio Chem, 1997; 272:19875-19879, Kemball-Cook et al., J Biol Chem, 1998; 273:8516-8521, Bharadwaj et al., J Biol Chem, 1996; 271:30685-30691, Ruf et al., Biochemistry, 1999; 38:1957-1966; WO 99/20767; WO 00/11416; WO 02/22776; WO 02/38162; WO 01/83725; WO 01/58935; U.S. Pat. No. 5,580,560.
Reports exist on expression of FVII in BHK or other mammalian cells (WO 92/15686, WO 91/11514 and WO 88/10295) and co-expression of FVII and kex2 endoprotease in eukaryotic cells (WO 00/28065).
Commercial preparations of human recombinant FVIIa are sold as NovoSeven®. NovoSeven® is indicated for the treatment of bleeding episodes in hemophilia A or B patients. NovoSeven® is the only rhFVIIa for effective and reliable treatment of bleeding episodes available on the market.
An inactive form of FVII in which arginine 152 and/or isoleucine 153 is/are modified has been reported in WO91/1154. These amino acids are located at the activation site. WO 96/12800 describes inactivation of FVIIa by a serine proteinase inhibitor; inactivation by carbamylation of FVIIa at the α-amino acid group I153 has been described by Petersen et al., Eur J Biochem, 1999; 261:124-129. The inactivated form is capable of competing with wild-type FVII or FVIIa for binding to tissue factor and inhibiting clotting activity. The inactivated form of FVIIa is suggested to be used for treatment of patients being in hypercoagulable states, such as patients with sepsis, in risk of myocardial infarction or of thrombotic stroke.
A circulating rhFVIIa half-life of 2.3 hours was reported in “Summary Basis for Approval for NovoSeven®”, FDA reference number 96-0597. Relatively high doses and frequent administration are necessary to reach and sustain the desired therapeutic or prophylactic effect. As a consequence adequate dose regulation is difficult to obtain and the need of frequent intravenous administrations imposes restrictions on the patient's way of living.
In connection with treatment of uncontrolled bleedings, such as trauma, it is believed that factor VIIa is capable of activating factor X to factor Xa without binding to tissue factor, and this activation reaction is believed to occur primarily on activated blood platelets (Hedner et al. Blood Coagulation & Fibrinolysis, 2000; 11; 107-111). However, hFVIIa or rhFVIIa has a to low activity towards factor X in the absence of tissue factor and, consequently, treatment of uncontrolled bleeding, for example in trauma patients, requires relatively high and multiple doses of hFVIIa or rhFVIIa. Therefore, in order to treat uncontrolled bleedings more efficiently (to minimize blood loss) there is need for improved FVIIa molecules, which possess a high activity toward factor X in the absence of tissue factor. Such improved FVIIa molecules will exhibit a lowered clotting time (or faster action) as compared to rhFVIIa when administered in connection with uncontrolled bleedings.
A molecule with a longer circulation half-life would decrease the number of necessary administrations. Given the association of current the rhFVIIa product with frequent injections, and the potential for obtaining more optimal therapeutic FVIIa levels with concomitant enhanced therapeutic effect, there is a clear need for improved FVII- or FVIIa-like molecules.
One way to increase the circulation half-life of a protein is to ensure that renal clearance of the protein is reduced. This may be achieved by conjugating the protein to a chemical moiety, which is capable of conferring reduced renal clearance to the protein.
Furthermore, attachment of a chemical moiety to the protein or substitution of amino acids exposed to proteolysis may effectively block a proteolytic enzyme from contact leading to proteolytic degradation of the protein, Polyethylene glycol (PEG) is one such chemical moiety that has been used in the preparation of therapeutic protein products. WO 98/32466 suggests that FVII, among many other proteins, may be PEGylated but does not contain any further information in this respect WO 01/58935 discloses a new strategy for developing FVII or FVIIa molecules having inter alia an increased half-life.
As indicated above, another problem in current rhFVIIa treatment is the relative instability of the molecule with respect to proteolytic degradation. Proteolytic degradation is a major obstacle for obtaining a preparation in solution as opposed to a lyophilized product. The advantage of obtaining a stable soluble preparation lies in easier handling for the patient, and, in the case of emergencies, quicker action, which potentially can become life saving. Attempts to prevent proteolytic degradation by site directed mutagenesis at major proteolytic sites have been disclosed in WO 88/10295.
One object of the present invention is to provide improved FVII or FVIIa molecules (FVII or FVIIa variants) with a longer circulation half-life (thereby decreasing the number of necessary administrations) and which are capable of activating factor X to factor Xa (without binding to tissue factor) more efficiently than hFVIIa or rhFVIIa (thereby being able to treat uncontrolled bleedings, such as a trauma, more efficiently).
Another object of the present invention is to provide improved FVII or FVII molecules (FVII or FVIIa variants) with an increased bioavailability (such as an increased Area Under the Curve as compared to rhFVIIa when administered intravenously) and which are capable of activating factor X to factor Xa (without binding to tissue factor) more efficiently than hFVIIa or rhFVIIa (thereby being able to treat uncontrolled bleedings, such as a trauma, more efficiently).
These objects are met by the FVII or FVIIa variants provided herein.